The present invention relates to liquid cleansing compositions having enhanced antimicrobial effectiveness. More specifically, the invention relates to specific polyvalent metal ions which improve antibacterial activity when used in liquid cleansing formulations. Neither the metals alone or the compositions alone provide the observed effect.
There is a large demand in the market for mild liquid cleansing formulations which additionally have an antibacterial effect. Antibacterial cleansers are preferred because they kill germs and mild personal cleansers are preferred to minimize skin irritation, dryness, etc. However, the combination of mild cleansing formulations and strong antibacterial effect is difficult to achieve. Thus, for example, while soaps provide antibacterial effects, they are not mild to the skin. When very mild non-soap surfactants are used, antibacterial effect is greatly compromised.
The balancing act between providing mildness and antibacterial effectiveness is recognized for example in International Publication WO 92/18100. In this publication, improved clinical mildness is said to be provided through the use of a water soluble cationic polymer (see page 10, lines 24-29). Cationic polymer is apparently used instead of additional ethoxylated surfactant because the percent of mild ethoxylated surfactant must be minimized in order not to affect antibacterial effectiveness (page 7, lines 4-6).
Another approach to providing mildness effect without affecting antibacterial properties is that which appears to be used by Dial in, for example, Liquid Dial Plus with Moisturizers Antibacterial Soap.RTM.. Here, mildness benefits are apparently provided by the use of moisturizing compounds rather than by the use of very mild surfactants alone (which, as indicated above, compromises antibacterial effectiveness).
In both cases, it can be readily seen that t is extremely difficult to provide effective antibacterial action in the presence of very mild surfactants. Rather, it is necessary to minimize the presence of those mild surfactants, by using larger amounts of harsher surfactants or soaps, and to mask the effects of the harshness by providing cationic mildness conditioning agents (WO 92/18100) or moisturizers (as in the Dial product).
It would be greatly beneficial if antibacterial effectiveness could be provided by polyvalent metal cation or cations which alone or together provide synergistic antimicrobial efficacy when used with liquid cleansing formulations (which themselves may or may not already contain an antibacterial agent), even in compositions with very mild surfactant systems.
Polyvalent cations such as zinc, copper, tin and aluminum are known antimicrobial agents and have long been used in cosmetic, dental and pharmaceutical applications (see, for example, S.S. Block, "Sterilization and Preservation", 1983; JP 63,250,309 and U.S. Pat. No. 5,037,634 to Williams et al.; see also U.S. Pat. No. 4,332,791 to Raaf et al.)
In particular, cations such as zinc ions have long been used in compositions for inhibiting plaque and/or calculus formation (U.S. Pat. No. 4,022,880 to Vinson et al. and U.S. Pat. No. 4,656,031 to Lane et al.). Copper ions have been used to stop fungal growth in bathtubs and ceramics (U.S. Pat. No. 3,992,146) and, in general, as disinfectants (U.S. Pat. No. 4,923,619).
In none of these references is it taught or suggested that one or more polyvalent metal cation or cations be used, i.e., in mild, liquid skin cleansing compositions by acting synergistically with the mild compositions to provide antibacterial activity.
Unexpectedly, applicants have now found that one or more polyvalent cation or cations (i.e., zinc, copper, tin, iron aluminum, cobalt, nickel, chromium, titanium and/or manganese) may be used to synergistically provide an antibacterial effect when used in mild, liquid skin cleansing compositions.